Method and apparatus for writing and reading optical recording medium

ABSTRACT

An apparatus for writing on and reading an overwritable optical disk comprises an identifier detector that identifies a recording condition in the sector to be overwritten, and a delay time controller circuit that sets a variation range of the start point for writing according to the recording condition. The record timing of the modulated data signal is changed at random within the set variation range when overwriting the sector of the optical disk.

This application is a Continuation of application Ser. No. 08/864,770,filed May 29, 1997, now U.S. Pat. No. 6,031,800, which application isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for writing onand reading an optical recording medium.

Recently, optical disks, cards and tapes are developed and have beenused for recording information optically. Especially, optical disks aregiven attention as a medium having large capacity and high density.

A conventional method for writing an optical disk is explained belowreferring to the figures. FIG. 27 shows an example of an optical diskusing a phase-change type recording film. A substrate 2301, which ismade of a glass or plastic material such as PMMA or polycarbonate, isprovided with guide grooves 2302 and pits indicating an address or otherinformation. This area with the pit train is called the ID area. Theguide grooves are formed in concentric circles or a coil from the innerto outer portions of the substrate. Areas 2307 between the grooves arecalled lands. The ID areas are located at a predetermined pitch alongthe guide grooves. The areas between the ID areas are called sectors. Asurface of the substrate 2301 is provided with layers of a protectivefilm 2303, a recording film 2304 and a reflection film 2305 formed bysputtering or other methods. Furthermore, a protective sheet is gluedonto the layers.

A method for writing on and reading the above-mentioned opticalrecording medium is explained below referring to the figures. FIG. 28shows a block diagram of a conventional writing and reading apparatus.FIG. 29 shows the write and read operation for an optical disk. In FIG.29, (a) indicates a write data signal, (b) indicates a laser-drivingsignal (corresponding to a laser power), (c) indicates a recorded stateof the optical disk, and (d) indicates a record format.

The reading process for the optical disk is performed as follows. Asystem controller circuit 101 drives a spindle motor 114 that rotatesthe optical disk 113. An optical head 112 focuses a laser beam with aweak power (Pr in FIG. 29) to irradiate the optical disk 113, trackingthe guide groove 2302 and the pit train 2502 shown in (c) of FIG. 29.The intensity of the beam reflected by the optical disk 113 varies inaccordance with the existence of the pit train 2502 and record marks2501. Detecting the intensity of the reflected beam generates readsignal 122, which is processed into binary data by a read signalprocessor circuit 115 and demodulated by a demodulator circuit 116. Thenthe signal is processed in an error correction and deinterleavingcircuit 117 to obtain read data. The deinterleaving process restores theoriginal data from the interleaved data, which are changed in order.

The writing process for the optical disk is performed as follows. Asystem controller circuit 101 connected to a host computer gives writedata 102 to an error correction and interleaving circuit 103, which addserror correcting data, i.e., parity bits to the write data, and performsan interleaving process. The interleaving process makes error correctioneasy by converting a burst error (long continuous error) due to a defectof the optical disk into a random error (short error). The write dataare divided into blocks and the order of the blocks is changed accordingto a predetermined rule in the interleaving process. Then a modulatorcircuit 104 modulates the data in accordance with the (1, 7) RLLmodulation method, for example. Consequently, a modulated data signal105 is obtained for writing the data area 604 shown in (d) of FIG. 29.

In the synthesizer circuit 109, each data block to be written into eachsector is provided with VFO and RESYNC signals from a synchronizingsignal generator circuit 108 as well as dummy data from a dummy datagenerator circuit 107 if necessary, to make the write data signal 118.The VFO and RESYNC are synchronizing signals for generating a clocksignal synchronizing with the read signal in a PLL circuit(synchronizing signal generator) in the read signal processor circuit115. The VFO signal is added to the head of the modulated data, and theRESYNCH signal is added in the modulated data signal at a predeterminedinterval. The dummy data are added for reducing a deterioration of therecording film generated at the end of writing when writing on the samesector repeatedly. The dummy data is not required to include anyinformation. The example of the write data signal 118 is shown in (a) ofFIG. 29.

Corresponding to the write data signal 118, the laser driver circuit 110generates a laser driving signal 111 to drive a laser in the opticalhead 112, modulating the intensity of the laser beam. An example of thelaser-driving signal 111 is shown in (b) of FIG. 29.

When the optical head 112 irradiates the recording film of the opticaldisk 113 with the focused laser beam having a high intensity (Pp shownin (b) of FIG. 29) for a predetermined period, the temperature of therecording film rises above the melting point and drops rapidly. As aresult, the melted spot becomes a recorded mark 2501 (shown in (c) ofFIG. 29) having an amorphous state due to rapid cooling. On thecontrary, when the recording film is irradiated with the focused laserbeam having a middle intensity (Pb shown in (b) of FIG. 29) for apredetermined period, the temperature of the recording film rises to thetemperature below the melting point but above the crystallization point.Then the irradiated spot is cooled gradually and assumes a crystallinestate.

A recorded pattern having crystalline and amorphous spots as mentionedabove, which corresponds to the modulated data signal 105, is created inthe data area 604 on the guide groove 2302. Thus, writing and reading ofinformation are performed using a difference of reflectivity between thecrystalline and amorphous states.

As shown in (d) of FIG. 29, there is a gap area 602 between the ID area601 and the VFO area 603, as well as a buffer area 606 between the dummydata area 605 and the next ID area 601. The gap area 602 generates atime for controlling the laser power, and the buffer area 606compensates for a difference of recording position due to rotationvariability of the spindle motor.

When scanning an ID area 601 between sectors 607 of the optical disk,address data are read by the laser irradiating the optical disk with thesame weak power as the reading power.

The system controller circuit has a configuration shown in FIG. 30.Transmission of write data and read data between a host computer and thewrite/read apparatus is performed using a write data buffer 2601 andread data buffer 2602 respectively. The read data is given to the readdata buffer 2602 as well as an address data detector circuit 2603. Anaddress data detecting signal is transmitted to the write data buffer2601 and the read data buffer 2602. A motor driver circuit 2604 drivesthe spindle motor.

When writing on the optical disk repeatedly as mentioned above, aquality of the read signal of the written data in a sector may bedeteriorated at a certain part. Especially, writing similar data intothe same sector repeatedly makes the deterioration serious because thatpart of the sector undergoes repeated melting and hardening whileanother part never melts. As a result, the thickness of the recordingfilm changes at the boundary of the two parts, so that the thermal andoptical characteristics are deteriorated at the boundary. In this case,it is difficult to record (write) and reproduce (read) data properly.

There is a writing method to solve the above-mentioned problem proposedin the Japanese laid-open patent application (Tokukaihei) 2-94113. Thismethod writes data while varying the start point for writing a sector atrandom within a predetermined range. This range is called the variationrange in this specification.

In this writing method, however, the variation range of the start pointfor writing was constant for various recording media or conditions. Onthe other hand, the deterioration rate of the recording film depends notonly on the number of repeating writings but also on the recordingmedium or recording condition.

Therefore, the above-mentioned writing method in the prior art is notenough for improving the deterioration of the recording film in everycase. For example, when overwriting the optical disk, the whole sectoris overwritten. Therefore, even if the data to be written are only asmall part of the sector, the whole sector is overwritten actually. Adirectory area of the disk is overwritten repeatedly with similar data.Thus, the directory area has a tendency to have its recording filmdeteriorated earlier than another area (called the general area in thisspecification).

Increasing the variation range of the start point for writing may reducethe deterioration of the recording film. However, an area for writingVFO or dummy data is decreased in a sector because the data area shouldbe settled in the sector. In other words, when adding the VFO area forgenerating synchronizing data to the head of the data area, and addingthe dummy data area to the tail of the data area, the length of the VFOarea or the dummy data area have to be shortened in accordance with theenlarged variation range of the start point for writing. Therefore, thedeterioration of the recording film at the start and end points of thesector may become critical when being written repeatedly, so thatreading of the written data becomes difficult at a certain deteriorationlevel of the recording film. As a result, the number of overwriting ofthe optical disk may be lowered.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for writing on andreading an optical recording medium, which can relieve a deteriorationof the recording film properly and increase the number of overwritingsby changing the variation range of the start point for writing inaccordance with the writing condition.

A method according to the present invention comprises the steps ofconverting write data into a modulated data signal corresponding to arecord pattern on the recording medium, selecting a first or secondwrite timing, altering the start point for writing the modulated datasignal at random within a first variation range in a sector if the firstwrite timing is selected, and altering the start point for writing themodulated data signal at random within a second variation range that islarger than the first variation range in a sector if the second writetiming is selected.

As mentioned above, the variation range of the start point for writingis set in accordance with a recording medium or recording conditions.Thus, deterioration at the specific part of the recording film isrelieved when writing repeatedly, and the number of overwritings isincreased by enlarging the variation range in the case of a criticalrecording method or medium. On the other hand, the number ofoverwritings can be increased by lengthening the VFO area or the dummydata area for suppressing the deterioration at the head or tail part ofthe sector in the case of the recording method or medium that generateslittle deterioration of the recording film due to repeated writing. Theinformation of the recording condition or medium can be prerecorded inthe medium as an identifier. Alternatively, the variation range can bealtered in accordance with the modulation method of the write data orthe recording condition such as overwriting frequency of the sector,whether the sector is directory area or not, or whether the sector is onthe guide groom or on the land (between the guide grooves).

A second method according to the present invention comprises thefollowing steps for recording and reproducing. The writing stepscomprise selecting one of two or more different methods for convertingwrite data into converted data, writing an identifier for identifyingthe method used as the converting method, together with the converteddata into an optical recording medium. The reproducing steps comprisereading the converted data and the identifier from the optical recordingmedium, and selecting one of two or more methods for restoring theoriginal data from the read data in accordance with the identifier.According to this method, the write data signals have different patternsby changing an order of blocks even if the same write data are writteninto the same part of the optical recording medium repeatedly. As aresult, a damage at a specific part of the recording film can bedispersed, and a deterioration of the recording film due to repeatedoverwriting can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram of a writing and reading apparatus accordingto a first embodiment of the present invention;

FIG. 2 is a flow chart showing a process for overwriting a sector of theoptical disk in the apparatus shown in FIG. 1;

FIG. 3 is a block diagram of a system controller circuit of theapparatus shown in FIG. 1;

FIG. 4 shows an example of a delay time controller circuit of theapparatus shown in FIG. 1;

FIG. 5 shows another example of a delay time controller circuit of theapparatus shown in FIG. 1;

FIG. 6A is a graph showing the relationship between a variation range ofthe start point for writing in a general area and an error rate;

FIG. 6B is a graph showing the relationship between a variation range ofthe start point for writing in a directory area and an error rate;

FIG. 7 (including subparts a-b) shows a record format when the variationrange of the start point for writing was set at 16 T in the apparatusshown in FIG. 1;

FIG. 8 (including subparts a-c) shows a record format when the variationrange of the start point for writing was set at 160 T in the apparatusshown in FIG. 1;

FIG. 9 is a block diagram of a variation of the writing and readingapparatus shown in FIG. 1;

FIG. 10 is a flow chart showing a process for overwriting a sector ofthe optical disk in the apparatus shown in FIG. 9;

FIG. 11 (including subparts a-b) shows a record format when thevariation range of the start point for writing was set at 16 T in theapparatus shown in FIG. 9;

FIG. 12 (including subparts a-c) shows a record format when thevariation range of the start point for writing was set at 160 T in theapparatus shown in FIG. 9;

FIG. 13 is a block diagram of another variation of the writing andreading apparatus shown in FIG. 1;

FIG. 14 is a block diagram of another variation of the writing andreading apparatus shown in FIG. 1;

FIG. 15 is a block diagram of a writing and reading apparatus accordingto a second embodiment of the present invention;

FIG. 16 is a flow chart showing a process for overwriting a sector ofthe optical disk in the apparatus shown in FIG. 15;

FIG. 17 is a flow chart showing a process for reproducing data writtenin a sector in the apparatus shown in FIG. 15;

FIG. 18 (including subparts a-b) shows write data before permutation andthe data after permutation in the apparatus shown in FIG. 15;

FIG. 19 (including subparts a-b) shows read data before restoring andthe data after restoring in the apparatus shown in FIG. 15;

FIG. 20 is a block diagram of a permutation method decision circuit anda permutation circuit of the apparatus shown in FIG. 15;

FIG. 21 is a block diagram of a permutation data detector circuit and arestoring circuit of the apparatus shown in FIG. 15;

FIG. 22 is a block diagram of a system controller circuit of theapparatus shown in FIG. 15;

FIG. 23 is a block diagram of a variation of the writing and readingapparatus shown in FIG. 15;

FIG. 24 (including subparts a-d) shows an example of interleaving anddeinterleaving operations in the apparatus shown in FIG. 23;

FIG. 25 is a block diagram of another variation of the writing andreading apparatus shown in FIG. 15;

FIG. 26 (including subparts a-d) shows an example of bit shift andreverse bit shift operations in the apparatus shown in FIG. 25;

FIG. 27 is a cross section of an optical disk using a phase-change typerecording film in the prior art;

FIG. 28 is a block diagram of a writing and reading apparatus in theprior art;

FIG. 29 (including subparts a-d) shows write data, modulated laserpower, record mark and record format in the prior art;

FIG. 30 is a block diagram of a system controller circuit of theapparatus shown in FIG. 28;

FIG. 31 is a block diagram of a variation of the apparatus shown in FIG.1;

FIG. 32 is a flow chart showing a process for overwriting a sector ofthe optical disk in the apparatus shown in FIG. 31;

FIG. 33 (including subparts a-c) shows a record format when thevariation range of the start point for writing was set at 160 T in theapparatus shown in FIG. 31;

FIG. 34 shows an example of a first delay time controller circuit of theapparatus shown in FIG. 31; and

FIG. 35 shows an example of a second delay time controller circuit ofthe apparatus shown in FIG. 31.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The writing and reading method and apparatus according to the presentinvention are further explained in detail using the figures andpreferred embodiments.

(First Embodiment)

FIG. 1 shows a block diagram of an apparatus for writing on and readingan optical recording disk according to a first embodiment of the presentinvention. FIG. 2 shows a flow chart for overwriting a sector of theoptical disk in the apparatus shown in FIG. 1. A system controllercircuit 101 that is connected to a host computer detects an address dataof a sector to be overwritten in the optical disk 113 (Step 201 in FIG.2). Then the system controller circuit 101 outputs write data 102 (Step202).

An error correction and interleaving circuit 103 adds error correctiondata to the write data, and performs an interleaving process (Step 203).The interleaved data is then modulated by a modulator circuit 104 (Step204). These operations are the same as the prior art shown in FIG. 28.

The modulator circuit 104 outputs the modulated signal 105, which issupplied to a delay time controller circuit 106. The delay timecontroller circuit 106 judges whether the area to be overwritten has ahigh frequency of overwriting, such as the directory area or not (Step205), and sets the variation range of the start point for writing to belarge in an area like the directory area (Step 206), or small in ageneral area (Step 207). The above-mentioned judgment is performedaccording to the identifier detected by an identifier detector circuit119. This identifier is prewritten in the ID area 601 (FIG. 29) or otherarea of each sector. The identifier detector circuit 119 detects theidentifier according to a predetermined timing generated by the systemcontroller circuit 101. The timing corresponds to the position of thewritten identifier in the optical disk 113, and outputs the detectedresult signal.

The delay time controller circuit 106 delays the modulated data 105 atrandom within a predetermined delay time corresponding to the variationrange set for the modulated data 105 (Step 208). The delay timecontroller circuit will be explained in detail later.

A synthesizer circuit 109 adds a synchronizing signal (VFO) generated bya synchronizing signal generator circuit 107 and dummy data generated bya dummy data generator circuit 108 to each data block to be written intoa sector, so as to generate a write data signal 118 (Step 209). Thewrite data signal 118 is supplied to a laser driver circuit 110, whichgenerates a laser driving signal 111 to drive a laser housed in anoptical head 112. After the intensity of the laser beam is modulated(Step 210), the laser beam irradiates the optical disk 133 for writingdata into the sector.

The system controller circuit has a configuration as shown in FIG. 3.This configuration differs from that of the prior art shown in FIG. 30in that an identification timing generator circuit 2701 supplies anidentification timing signal to the identifier detector circuit 119according to an address data and an address detection signal from anaddress data detector circuit 2603. The address data detecting signal isalso supplied to the delay time controller circuit 106.

FIG. 4 shows an example of the delay time controller circuit 106.Generally, a delay time controller circuit includes a write controlsection having two different write timings, and a selecting section forselecting one of the two write timings in accordance with theidentifier. In FIG. 4, the selecting section is a switching circuit 305.The write control section includes plural delay circuits 301, two clockgenerators 302, 303 that generate clock signals for the delay circuits301, and selector 304 that selects one of the delay circuits 301 forinputting the modulated data signal 105. Each delay circuit 301 includesshift registers, delay lines or counters.

The delay time controller circuit shown in FIG. 4 has two clockgenerator circuits 302, 303. The period of the clock generated by thefirst clock generator circuit 302 is T, and that generated by the secondclock generator circuit 303 is 10 T.

If the switching circuit 305 selects the first clock generator circuit302, the delay times of the delay circuits are 0, T, 2 T, 3 T, . . . ,16 T respectively (First write timing). On the contrary, if the secondclock generator circuit 303 is selected, the delay times of the delaycircuits 301 are 0, 10 T, 20 T, 30 T, . . . 160 T respectively (Secondwrite timing).

The actual operation of the delay time controller circuit 106 shown inFIG. 4 is as follows.

When writing on the general area of the optical disk 113, the switchingcircuit 305 selects the first clock generator circuit 302 according tothe signal 121 from the identifier detector circuit 119. The delaycircuits 301 generate corresponding delay times 0-16 T based on theperiod T of the first clock. The address detection signal 120 makes theselector 304 select one of delay circuits 301 at random. The selecteddelay circuit is maintained until the next address is detected.

When writing on the directory area of the optical disk 113, theswitching circuit 305 selects the second clock generator circuit 303according to the signal 121 from the identifier detector circuit 119.The delay circuits 301 generate corresponding delay times 0-160 T basedon the period 10 T of the second clock. The address detection signal 120makes the selector 304 select one of delay circuits 301 at random. Thus,the variation range of the start point for writing data can be alteredbetween the directory area and other area by changing the clock (periodstep) for the plural delay times.

FIG. 5 shows another example of the delay time controller circuit 106.In this circuit, the selecting section is a switching circuit 405. Thewrite control section includes plural delay circuits 401, a clockgenerator circuit 402 that generates a clock signal for the delaycircuits 401, and two selectors 403, 404 that select one of the delaycircuits 401 for inputting the modulated data signal 105 through theswitching circuit 405.

The delay times of the delay circuits 401 are 0, T, 2 T, 3 T, . . . 160T based on the clock period T. In other words, the step width is T, andthe total width is 160 T.

The delay time controller circuit shown in FIG. 5 has two selectors 403,404. If the switching circuit 405 selects the first selector 403, thewrite timing is altered at random within the delay time of 0-16 T (Firstwrite timing). If the switching circuit 405 selects the second selector404, the write timing is altered at random within the delay time of0-160 T (Second write timing).

The actual operation of the delay time controller circuit 106 shown inFIG. 5 is as follows.

When writing on the general area of the optical disk 113, the switchingcircuit 405 selects the first selector 403 according to the signal 121from the identifier detector circuit 119. The delay time is selected atrandom from 16 steps 0-16 T. The selected delay time is maintained untilthe next address is detected.

When writing on the directory area of the optical disk 113, theswitching circuit 405 selects the second selector 404 according to thesignal 121 from the overwrite frequency identifier detector circuit 119.The delay time is selected at random from 160 steps 0-160 T. Theselected delay time is maintained till detection of the next address.Thus, the variation range of the start point for writing can be changedbetween the directory area and other areas by changing the step numberof the plural delay times.

The following explanation is about an example for confirming the effectof this embodiment. The substrate of the optical disk 113 was made of apolycarbonate plate having a diameter of 130 mm and a thickness of 0.6mm. Pits are preformed on the substrate as address data, and guidegrooves on which data are to be written are formed in sector areas. Apitch of the guide grooves was 1.6 micron. Four layers, that is aprotective film, a photosensitive film, a protective film and areflection film were formed on the substrate by sputtering. Then, aprotective sheet was glued on the surface of the layers. The protectivefilm was made of ZnS--SiO₂, the photosensitive film was made ofTe--Sb--Ge, and the reflection film was made of Al.

The above-mentioned optical disk was rotated at a linear speed of 5 m/sby a spindle motor 113. A laser beam having a wavelength of 680 nm wasused for writing after being focused by an objective lens with anumerical aperture (N. A.) of 0.6.

Laser powers for writing and reading were set at Pp=10 mW, Pb=4 mW, andPr=1 mW. A method of (8-16) pulse width modulation was used formodulating the write data. The shortest mark length was 0.6 micron. Thedelay time controller circuit 106 was used, which selects the variationrange of the start point for writing by selecting the clock generatorcircuit 302 or 303 as shown in FIG. 4.

Under the above-mentioned conditions, the relationship between thevariation range of the start point for writing and an error rate of readdata is measured in each area. In the directory area, assuming similardata are to be written repeatedly in a real application, two patterns ofdata were written repeatedly and the variation range was set within0-160 T (0-10 T per a step). In the general area, thirty patterns ofdata were written repeatedly and the variation range was set within 0-64T (0-4 T per a step). The error rate of the read data was measured afteroverwriting 100,000 times.

FIG. 6A shows the relationship between the variation range of the startpoint for writing and the error rate after overwriting 100,000 times inthe general area. FIG. 6B shows the relationship between the variationrange of the start point for writing and the error rate afteroverwriting 100,000 times in the directory area.

As understood from FIGS. 6A and 6B, a better error rate afteroverwriting 100,000 times is obtained if the variation range of thestart point for writing becomes larger. It was also understood that theminimum variation range of the start point for writing in which the gooderror rate was obtained varied depending on the type of area (this meansa randomness of the write data).

In accordance with the above-mentioned result, the variation range ofthe start point for writing was set as follows. To obtain the error ratebelow 0.0005, the variation range of the start point for writing was setat 16 T (1 T per a step) in the general area, and at 160 T (10 T per astep) in the directory area (variable variation range case). Forcomparison, first and second fixed variation range cases were alsoperformed. In the first fixed variation range case, the variation rangewas set at 16 T (1 T per a step) in both the general and directoryareas. In the second fixed variation range case, the variation range wasset at 160 T (10 T per a step) in both the general and directory areas.

FIG. 7 shows a record format when the variation range of the start pointfor writing was set at 16 T. A clock for writing data was the same asthe clock for generating delay times. A data volume that can be writtenin a sector was 1000 bytes. Data lengths of the VFO area and dummy dataarea were both 15 bytes when the start point for writing didn't change.

In FIG. 7, (a) shows a record format in the case where the start pointfor writing didn't change. A data area 604 was provided with VFO 603 anddummy data 605 after being provided with a delay time by the delay timecontroller circuit 106, and then supplied to the laser driver circuit110 for generating the laser driving signal 111.

In FIG. 7, (b) shows a record format in the case where the start pointfor writing was shifted backward by 16 T (i.e., 1 byte). In this case,the laser-driving signal 111 was generated 16 T later than the case of(a). In the writing process with the variation range of 16 T, thegeneration timing of the laser driving signal corresponding to the dataarea varied within 16 T by means of the delay time controller circuit.As a result, the data written position in the sector varied within 16 T(1 byte).

FIG. 8 shows a record format when the variation range of the start pointfor writing was set at 160 T. In FIG. 8, (a) is a record format in thecase where the start point for writing did't change, (b) is in the casewhere the start point for writing was shifted forward by 80 T (i.e., 5byte), and (c) is in the case where the start point for writing wasshifted backward by 80 T (i.e., 5 byte). In the case (b), thelaser-driving signal 111 corresponding to the data area was generated 80T earlier than the case (a). In the case (c), the laser-driving signal111 corresponding to the data area was generated 80 T later than thecase (a).

In the writing process with the variation range of 160 T, the generationtiming of the laser-driving signal varied within 160 T by means of thedelay time controller circuit. As a result, the data written position inthe sector varied within 160 T (10 byte). The ID area in the opticaldisk predetermines the length of the sector. Therefore, if the gap area802 and the buffer area 806 have fixed lengths, the VFO and dummy dataareas can decrease in their lengths as the written position varies morewidely in the sector.

In the first fixed variation range case mentioned above, the variationrange was 1 byte in both the directory area and other areas. Therefore,the length of the VFO area or dummy data area varied within 15-16 bytesor 14-15 bytes. In other words, the shortest length of the VFO area orthe dummy data area was 14 or 15 bytes. Similarly, in the second fixedvariation range case, the variation range was 10 bytes in both thedirectory area and other areas. Therefore, the length of the VFO area ordummy data area varied within 10-20 bytes, and the shortest length ofthe VFO area or the dummy data area was 10 bytes.

On the other hand, in the variable variation range case mentioned above,in the directory area, the variation range of the start point forwriting was 10 bytes, so the lengths of the VFO area and the dummy dataarea varied within 10-20 bytes as shown in FIG. 8. The shortest lengthof the VFO area or the dummy data area was 10 bytes. In the generalarea, the variation range of the start point for writing was 1 byte, sothe length of the VFO area or the dummy data area varies within 15-16bytes (or 14-15 bytes). The shortest length of the VFO area or the dummydata area was 14 or 15 bytes.

Under the above-mentioned conditions, the following experiment wasperformed. Two patterns of data were written into the directory arearepeatedly, and thirty patterns of data were written into the generalarea repeatedly. Error states were investigated after overwriting 50,000times and 100,000 times.

Table 1 shows the comparison of the error state among the first fixedvariation range case, the second fixed variation range case and thevariable variation range case. In this table, "synchro error" means asynchronizing error state making the data reproduction impossible when aphase-locked loop (PLL) circuit becomes out of lock. Similarly, "readerror" means a state of improper error correction making the datareproduction impossible.

                  TABLE 1                                                         ______________________________________                                                  Variation range                                                                        After 50,000                                                                             After 100,000                                   ______________________________________                                        First fixed v.r. case                                                         General area                                                                               16T       OK         OK                                          Directory area                                                                            160T       read error read error                                  Second fixed v.r. case                                                        General area                                                                              160T       OK         synchro error                               Directory area                                                                            160T       OK         synchro error                               Variable v.r. case                                                            General area                                                                               16T       OK         OK                                          Directory area                                                                            160T       OK         synchro error                               ______________________________________                                    

As shown in Table 1, in the first fixed variation range case, thegeneral area could be overwritten 100,000 times with no error, but thedirectory area had a read error after 50,000 times of overwriting. Awaveform distortion was observed in the read signal of the directoryarea. It is estimated that the read error was generated because thevariation range of the start point was too small for the write data withsmall randomness, so a local deterioration of the recording film wasgenerated.

In the second fixed variation range case, both the general and directoryareas could be overwritten 50,000 times with no error, but had asynchronizing error after 100,000 times of overwriting. In the waveformof the read signal after 100,000 times of overwriting, at least 5 bytesof the VFO were missing. It is estimated that the synchronizing errorwas generated when the length of the VFO area became short since thevariation range of the start point was large, and the deterioration ofthe recording film at the start point in the sector caused an unlock ofthe PLL circuit since the deteriorated portion in the VFO area becamerelatively large.

On the other hand, in the variable variation range case, both thegeneral and directory areas could be overwritten 50,000 times with noerror, and the general area could be overwritten 100,000 times with noerror. The reason why the general area could be overwritten 100,000times with no error may be that the deteriorated portion in the VFO areabecame relatively small by decreasing the variation range of the startpoint for writing, and increasing the length of the VFO area in thegeneral area. In addition, since the variation range of the start pointfor writing was set large in the directory area, a local deteriorationof the recording film was hardly generated in the data area. Thus, thedirectory area could be overwritten 50,000 times without error.

As explained above, this embodiment of the present invention provides abetter method for writing and reading an optical recording medium, inwhich the variation range of the start point for writing can be changedin accordance with a write condition. Therefore, a local deteriorationof the recording film due to repeated overwriting can be reduced byenlarging the variation range in the directory area that has a tendencyto have its recording film deteriorated early due to repeatedoverwriting. Thus, the number of times of overwriting can be increased.In addition, in the general area where the deterioration of therecording film is little, the number of times of overwriting in thegeneral area can be further increased by lengthening the VFO and/ordummy data area for relieving a deterioration at the start and endpoints in the sector.

In FIG. 1, the delay time controller circuit 106 is located before thesynthesizer circuit 109. Alternatively, the delay time controllercircuit 106 may be located after the synthesizer circuit 109 as shown inFIG. 9. In this case, FIG. 10 shows a flow chart for overwriting asector of the optical disk. This flow chart differs from that shown inFIG. 2 in that the write data is delayed (Step 909) by the delay timecontroller circuit 106 after being provided with the VFO 603 and dummydata 605 (Step 905).

FIG. 11 shows a record format when the variation range of the startpoint for writing was set at 16 T. In FIG. 11, (a) shows a record formatin the case where the start point for writing didn't alter, and (b)shows a record format in the case where the start point for writing wasdelayed 16 T (i.e., 1 byte).

FIG. 12 shows a record format when the variation range of the startpoint for writing was set at 160 T. In FIG. 12, (a) is a record formatin the case where the start point for writing didn't alter, (b) is inthe case where the start point for writing was shifted forward by 80 T,and (c) is in the case where the start point for writing was delayed 80T.

These cases differ from the cases shown in FIGS. 7 and 8 in that all thestart points for writing the VFO 603, the data area 604 and the dummydata 605 were varied. As a result, an influence of the deterioration atthe start and/or end point of the sector is reduced, since the lengthsof the VFO and dummy data areas were not shortened.

A block diagram of a writing and reading apparatus as a variation ofthis embodiment is shown in FIG. 31. This apparatus includes first andsecond delay time controller circuits 3101, 3102 before and after thesynthesizer circuit 109. The first delay time controller circuit 3101delays the modulated data signal within the variation range of 0-144 T.The second delay time controller circuit 3102 delays the write datasignal within the variation range of 0-16 T. FIG. 32 shows a flow chartfor overwriting a sector of the optical disk in the apparatus shown inFIG. 31. This flow chart shown in FIG. 32 differs from that of FIG. 2 inthe following steps. The first delay time controller circuit 3101 delaysthe modulated data signal within the variation range of 0-144 T onlywhen the area to be written has a high frequency of overwriting (Step3206). After the VFO 603 and the dummy data 605 are added to the writedata (Step 3207), the second delay time controller circuit 3102 delaysevery data signal not depending on the frequency of overwriting, withinthe variation range of 0-16 T (Step 3208).

FIG. 34 shows an example of the first delay time controller circuit 3101of the apparatus shown in FIG. 31. In this block diagram, the selectingsection is a switching circuit 3406. The write control section 3405includes plural delay circuits 3401, a clock generator circuit 3402 thatgenerate clock signals for the delay circuits 3401, and selector 3403that selects one of the delay circuits 3401 for inputting the modulateddata signal 105.

The delay times of the delay circuits 3401 are set to 0, T, 2 T, . . . ,144 T respectively based on the clock period T. In other words, the stepwidth is T, and the total width is 144 T.

If the switching circuit 3404 selects the selector 3403, the writetiming is altered at random within the delay time of 0-144 T by one ofdelay circuits 3401 (First write timing). If the switching circuit 3404does not select the selector 3403, the write data is outputted directlywithout passing through any delay circuit. In this case, the delay timeis zero, and the write timing is constant (Second write timing).

The actual operation of the delay time controller circuit shown in FIG.34 is as follows. When writing on the directory area of the optical disk113, the switching circuit 3404 selects the selector 3403 according tothe signal 121 from the identifier detector circuit 119. The delay timeis selected at random from 144 steps 0-144 T. The selected delay time ismaintained until the next address is detected.

When writing on the general area of the optical disk 113, the switchingcircuit 3404 selects the direct pass to the output without passingthrough any delay circuit, so that the delay time is always zero.

FIG. 35 shows an example of the second delay time controller circuit3102 of the apparatus shown in FIG. 31. In this block diagram, the writecontrol section 3504 includes plural delay circuits 3501, a clockgenerator circuit 3502 that generate clock signals for the delaycircuits 3501, and selector 3503 that selects one of the delay circuits3501 for inputting the modulated data signal 105.

The delay times of the delay circuits 3501 are set to 0, T, 2 T, . . . ,16 T respectively based on the clock period T. In other words, the stepwidth is T, and the total width is 16 T.

In the actual operation, the delay time controller circuit shown in FIG.35 works as follows. In every recording area of the optical disk, i.e.,not depending on overwriting frequency, the selector 3503 selects one of16 delay times 0-16 T at random in accordance with the address detectionsignal 120 given by the system controller circuit. The selected delaytime is maintained until the next address is detected.

By using two delay time controller circuits shown in FIGS. 34 and 35,the number of steps of delay times can be changed, so that the variationrange of the start point for writing is changed between 160 T (144 T+16T) for the directory area and 16 T for the general area.

Record formats for this embodiment of FIG. 31 are explained below. Whenthe variation range of the start point for writing is 16 T, the recordformat is the same as shown in FIG. 11, in which (a) is in the casewhere the start point for writing didn't alter, and (b) is in the casewhere the start point for writing was delayed 16 T.

When the variation range of the start point for writing is 160 T, therecord format is as shown in FIG. 33. In this figure, (a) shows a recordformat in the case where the start point for writing was shifted forwardby 80 T, and (b) shows a record format in the case where the start pointfor writing was shifted backward (i.e., delayed) by 80 T. In thesecases, the start point for writing the VFO 603 and the dummy data 605varies within the variation range of one byte, and the start point forwriting in the data area varies within the variation range of ten bytes.

The configuration shown in FIG. 9 is preferable if the spindle motor 114has a small jitter, or the laser driver circuit 110 has a capability offast power control operation. On the contrary, if the jitter of thespindle motor 114 is not small, or the capability of the laser drivercircuit 110 is not high, it is preferable to adopt the configurationshown in FIG. 1, and to secure the constant gap area 602 and buffer area606 independently from the varying start point for writing as shown inFIGS. 7 and 8. The configuration shown in FIG. 31 ensures the gap area602 and the buffer area 606 properly. Any configuration shown in FIGS.1, 9 or 31 according to the present invention can enhance the number oftimes of overwriting.

Another method for high-density recording has been proposed, where landsbetween guide grooves are also used for recording. In this case, athermal stress generated at the periphery of the record mark isdifferent between the guide groove and the land because their sectionshave different shapes at the periphery of the record mark. Therefore,the level of a deterioration generated after overwriting is differentbetween the guide groove and the land even if the overwriting isrepeated same times.

To improve the above-mentioned problem, it may be preferable to adoptthe configuration of the writing and reading apparatus shown in FIG. 13.This configuration differs from that of FIG. 1 in that the delay timecontroller circuit 106 set the variation range of the start point forwriting in accordance with an identified result supplied from aland/guide groove identifier detector circuit 1201. In this case, thevariation range of the start point for writing in the land is setdifferent from that for writing in the guide groove, so that the numberof times of overwriting is enhanced.

A pulse width modulation method in which both edges of the record markhave information is also proposed for a high-density recording. However,in this pulse width modulation method the recording film tend to wearearlier than in the pulse position modulation method in which theposition of the record mark provides information, because the formerusually makes longer marks than the latter. Moreover, the pulse widthmodulation cannot reproduce data correctly if the edge of the recordmark is not detected precisely. Therefore, reproduction capability ofthe pulse width modulation is affected very much by the deterioration ofthe recording film. Thus, in the pulse width modulation it is moredifficult to reproduce data correctly than in the pulse positionmodulation under the same deterioration level of the recording film.

Considering such a problem, it is also preferable to adopt aconfiguration of the writing and reading apparatus as shown in FIG. 14.This configuration differs from that shown in FIG. 1 in that the delaytime controller circuit 106 sets the variation range of the start pointfor writing in accordance with a detection result by a modulation methodidentifier detector circuit 1301. In this case, the variation range ofthe start point for writing with the pulse width modulation is setdifferent from that for writing with the pulse position modulation, sothat the number of times of overwriting is enhanced.

The variation range of the start point for writing, the change stepnumber, the change interval, or the record format mentioned above is anexample, and the proper values should be selected for them according tothe recording condition or medium. In addition, the variation range ofthe start point for writing can be changed among three or more values bycombining the modulation method, the overwrite frequency, land/guide andother elements.

(Second embodiment)

FIG. 15 shows a block diagram of an apparatus for writing on andrecording an optical recording disk according to a second embodiment ofthe present invention. FIG. 16 shows a flow chart for overwriting asector of the optical disk in the apparatus shown in FIG. 15.

This embodiment differs from the prior art in the following process. Apermutation method decision circuit 1401 decides the permutation methodof the write data 102 at random (Step 1503). A permutation circuit 1402divides the write data into plural groups and changes the order of thegroups according to an instruction from the permutation method decisioncircuit 1401 to obtain converted data 1405 (Step 1504). The permutationcircuit 1402 also adds the permutation data as an identifier forrestoring original data from the converted data (Step 1505).

FIG. 17 is a flow chart showing a process of reproducing a data writtenin a sector. This process differs from that of the prior art in thefollowing steps. After error correction and deinterleaving (Step 1604),the permutation data detector circuit 1403 detects the permutation datathat is the identifier for restoring the original data (Step 1605). Arestoring circuit 1404 restores the original data based on theidentifier (Step 1606).

An example of the permutation and restoring of data is explained belowusing FIGS. 18 and 19.

The division and permutation of write data are performed as follows.Dividing positions are determined at random concerning a series of writedata shown in (a) of FIG. 18. Then the series of write data is divided,changed in order, and provided with permutation data as an identifiershowing the divided position, so as to make a series of data shown in(b) of FIG. 18. For example, if the write data are divided at the 20thbyte and changed in order (this means a conversion method), anidentifier showing the 20th byte is added to the converted data. It isnot required to write the identifier into every sector. The identifiermay be written into the directory (directory) area. The conversionmethod is not required to be changed for each sector, but can be samefor plural sectors in a serial writing. Then, the error correction dataare added and the interleave process is performed.

As shown in (a) of FIG. 19, when reproducing data, after errorcorrection and deinterleaving, the identifier, i.e., permutation data,added to the tail of the converted data, are detected. For example, ifthe permutation data show the 20th byte, the last 20 bytes of theconverted data are divided and added to the head of the data (this meansa restoring method), so that the original data are obtained as shown in(b) of FIG. 19

The dividing position is determined at random by the permutation circuit1402 at every writing of a sector, so a different modulated data signalis used for each writing even if the same data are written into the samesector repeatedly. As a result, the optical disk 113 is written withdifferent write data signals except the VFO and RESYNC areas. Therefore,a probability of forming a record mark 2501 on the guide groove 2303 issubstantially uniform in a sector of the optical disk 113. Thus, localdamage of the recording film due to repeated overwriting is relieved.

FIG. 20 shows an example of the permutation method decision circuit 1401and the permutation circuit 1402. In this figure, a random numbergenerator 2901 generates random numbers, when being triggered by apermutation-timing signal. If each sector of the optical disk isaccessed at random, a usual counter circuit can be used instead of therandom number generator to obtain the same effect. An address presetcircuit 2902 gives an initial memory address to a memory 2903 forreading the memory 2903. In the above-mentioned example, the initialmemory address is an address corresponding to 20th byte from the head ofthe write data stored in the memory 2903. The memory 2903 stores thewrite data and outputs the stored data from the given initial memoryaddress to the tail address and the remaining part of the data from thehead address in order. Thus, the memory 2903 outputs the converted data.A synthesizer circuit 2904 add an identifier indicating the initialmemory address to the data.

FIG. 21 shows an example of the permutation data detector circuit 1403and the restoring circuit 1404. A detector circuit 3001 detects theidentifier from the decoded data after error correction anddeinterleaving. A hold circuit 3002 holds the identifier and outputs thesame to an address preset circuit 3003 until the next identifier isdetected. The address preset circuit 3003 gives an initial memoryaddress to a memory 3004. In the example mentioned above, the initialmemory address is an address corresponding to 20th byte from the tail ofthe converted data stored in the memory 3004. The memory 3004 stores theconverted data and outputs the stored data from the given initial memoryaddress to the tail address and the remaining part of the data from thehead address in order. Thus, the memory 3004 outputs the restored data.

FIG. 22 shows the system controller circuit of this embodiment. Thiscircuit differs from that of the prior art in that a permutation timinggenerator circuit 2801 outputs a permutation timing signal to thepermutation method decision circuit 1401 in accordance with the addressdata and the address data detecting signal from the address datadetector circuit 2603.

The following explanation is about an example for confirming the effectof this embodiment. The substrate of the optical disk 113 was made of apolycarbonate plate having a diameter of 130 mm. Pits are preformed onthe substrate as address data, and guide grooves for writing are formedin sector areas. Four layers, that is a protective film, aphotosensitive film, a protective film and a reflection film were formedon the substrate by sputtering. Then, a protective sheet was glued onthe surface of the layers.

The protective film was made of ZnS--SiO₂, the photosensitive film wasmade of Te--Sb--Ge, and the reflection film was made of Al. This opticaldisk was rotated at a linear speed of 5 m/s by the spindle motor 113. Alaser beam having a wavelength of 680 nm was used for writing, afterbeing focused by an objective lens with a numerical aperture (N. A.) of0.6. Laser powers for writing and reading were set at Pp=10 mW, Pb=4 mW,and Pr=1 mW. A method of (8-16) pulse width modulation was used formodulating the write data. The shortest mark length was 0.6 micron.

According to the above-mentioned condition, the write data wereoverwritten 100,000 times into the same sector. The error rate ofdemodulated data was measured for each overwriting with two methods forcomparison. The first method used the permutation by dividing the writedata and changing the order according to the present invention. Thesecond method didn't use the permutation as the prior art. In bothmethods, the write data for a sector includes 500 bytes. In the firstmethod using the permutation, the dividing position was selected atrandom by a step of one byte. The measured result is shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                   Error rate after 100,000 times overwrite                           ______________________________________                                        Without permutation                                                                        0.011                                                            With permutation                                                                           0.000002                                                         ______________________________________                                    

As shown in Table 2, the first method with the permutation has smallererror rate than the second method without permutation, so that thenumber of times of overwriting is enhanced.

As mentioned above, according to the writing and reading method of theoptical recording medium according to this embodiment of the presentinvention, the write data signals have different patterns by convertinginto plural patterns even if the same write data are written into thesame sector of the optical recording medium repeatedly. As a result, adamage at a specific part of the recording film can be dispersed, and adeterioration of the recording film due to repeated overwriting can bereduced.

The number of divided blocks and other parameter in this embodiment isan example, and should be selected adequately in accordance with therecord condition or medium.

The method for dividing a series of write data should not be limited tothe example mentioned in this embodiment, but may be any method that canconvert write data into plural different converted data.

For example, as shown in FIG. 23, a different interleaving method can beused by adding another pair of interleaving circuit and deinterleavingcircuit to the configuration of FIG. 15. In the configuration shown inFIG. 23, one of two error correction and interleaving circuits 103, 1903is selected by a first selecting circuit 1902 at random controlled by aninterleaving method decision circuit 1901, and an identifier indicatingthe selected method is added to the converted data in the recordingprocess. In the reproducing process, one of two error correction anddeinterleaving circuits 117, 1904 is selected by a second selectingcircuit 1905 according to the identifier detected by an interleavingmethod detector circuit 1906. The interleaving method decision circuit1901 includes a random number generator circuit or a counter circuit inthe same way as the permutation method decision circuit shown in FIG.15.

FIG. 24 shows an example of interleaving and deinterleaving operations.In FIG. 24, (a) shows write data before interleaving, (b) shows the dataafter interleaving and provided with an identifier indicating theinterleaving method, (c) shows read data before deinterleaving, and (d)shows data after deinterleaving in accordance with the detectedidentifier. In this case, the same process as the interleaving canperform division and permutation of the write data, so that theconfiguration of the writing and reading apparatus can be simplified.

The method for converting a series of write data into one of two or moredifferent series of converted data may be the following method.

FIG. 25 shows a configuration for generating a series of converted datafrom a series of write data by a scrambling method, which comprises abit shift process of the write data. In the recording process, a bitshift method decision circuit 2101 decides a shift bit number at random,and a bit shift circuit 2102 performs the bit shift process by a unit ofone or more bits according to the decided shift bit number to obtainconverted data 1405. An identifier indicating the shift bit number isadded to the converted data. These steps correspond to the convertingmethod. In the reproducing process, a bit shift identifier detectorcircuit 2103 detects the identifier, and a reverse bit shift circuit2104 performs the reverse bit shift process by a unit of one or morebits according to the detected identifier. These steps correspond to therestoring method. The bit shift method decision circuit 2101 includes arandom number generator circuit or a counter circuit in the same way asthe permutation method decision circuit shown in FIG. 15.

FIG. 26 shows an example of the bit shift and reverse bit shiftoperations. In FIG. 26, (a) shows write data before bit shift, (b) showsthe data after bit shift and provided with an identifier indicating thebit shift method, (c) shows read data before reverse bit shift, and (d)shows data after reverse bit shift in accordance with the detectedidentifier. In this case, a large memory for permutation is notrequired, so that the configuration of the writing and reading apparatuscan be simplified.

In the second embodiment, by changing the start point for writing asector with a modulated data signal at random, the RESYNC area includedin the data area can also be written in a different position, so thenumber of times of overwriting is further enhanced.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, all changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

What is claimed is:
 1. An apparatus for writing data on and reading datafrom an overwritable optical recording medium having a sector format,comprising:a modulator portion modulating data to make a modulated datasignal corresponding to a record pattern of an optical recording medium;a synchronizing signal generating portion generating a synchronizingsignal to be added before the modulated data signal; a dummy datagenerating portion generating dummy data to be added after the modulateddata signal; a delay portion performing a first function of delaying astart point for writing the modulated data signal into a sector on anoptical recording medium at random within a first variation range, and asecond function of delaying a start point for writing the modulated datasignal into a sector on an optical recording medium at random within asecond variation range that is larger than the first variation range;and a switching portion selecting one of the first function and thesecond function of the delay portion; wherein a start point for writingthe synchronizing signal on an optical recording medium is delayedwithin a synchronizing signal variation range that is smaller than avariation range of a start point for writing the modulated data signal,and a length of the dummy data is changed in accordance with a startpoint for writing the modulated data signal.